A member for a high-temperature apparatus such as a moving blade or a stationary blade of a jet engine or a gas turbine, and a boiler tube often has a surface subjected to coating in order to enhance heat resistance and corrosion resistance.
Generally, in order to enhance the heat resistance of a base material (alloy), the base material is subjected to ceramic coating referred to as thermal barrier coating (hereinafter, referred to as “TBC”). In this process, a ceramic layer having a thermal expansion coefficient significantly different from that of the base material is easily exfoliated from the surface of the base material according to temperature change. Therefore, an alloy layer referred to as an undercoat layer (bond coat layer) is inserted between the ceramic layer and the base material in order to enhance the adhesion of the ceramic layer and base material. However, since atoms move (diffuse) between the undercoat layer and the base material under an ultrahigh temperature environment of 800 to 1200° C., the undercoat layer will lose its characteristics over time. As a result, an Al2O3+NiAl2O4 layer having low protection performance is formed near the interface between the undercoat layer and the base material, and an internal corrosion layer which have internal oxide and internal nitride and an Al depleted layer are formed inside the base material. Thus, the TBC causes a problem that the characteristics of the undercoat layer are lost over time under an ultrahigh temperature environment and the mechanical characteristics (strength, creep resistance, fatigue resistance) of the base material are also lost.
On the other hand, in order to enhance corrosion resistance, an oxide film protecting the base material is formed by diffusion coating of Al, Cr, Si or the like or overlay coating of a high Ni-high Cr alloy, a MCrAlY (M=Ni, Co, Fe) alloy or the like. However, since the diffusion of atoms contributing to corrosion resistance is remarkably fast under an ultrahigh temperature environment of 800 to 1200° C., the oxide film protecting the base material is lost over time. Thus, the diffusion coating or the overlay coating causes a problem that the oxide film protecting the base material is lost over time under an ultrahigh temperature environment and thereby the mechanical characteristics of the base material are also lost.
As means for eliminating these problems, alloy films containing a Re-based alloy layer are disclosed (Patent Documents 1 to 13, Non-patent Documents 1 to 3). Since a Re-based alloy can suppress the diffusion of atoms constituting a base material and an alloy film, the Re-based alloy functions as a diffusion barrier which can eliminate the problems. For example, when the TBC is applied to the surface of the base material, the insertion of a film (barrier layer 30) made of a Re-based alloy between base material 10 and undercoat layer 20, as shown in FIG. 1, can prevent the atoms of undercoat layer 20 from moving into base material 10 and the atoms of base material 10 from moving into undercoat layer 20. As a result, the characteristics of the undercoat layer and the base material can be maintained even under an ultrahigh temperature environment for some amount of time.    Patent Document 1: U.S. Pat. No. 6,306,524    Patent Document 2: U.S. Pat. No. 6,746,782    Patent Document 3: U.S. Pat. No. 6,830,827    Patent Document 4: Japanese Patent No. 3708909    Patent Document 5: Japanese Patent No. 3765292    Patent Document 6: Japanese Patent No. 3810330    Patent Document 7: Japanese Patent Application Laid-Open No. 2001-323332    Patent Document 8: Japanese Patent Application Laid-Open No. 2003-213479    Patent Document 9: Japanese Patent Application Laid-Open No. 2003-213480    Patent Document 10: Japanese Patent Application Laid-Open No. 2003-213481    Patent Document 11: Japanese Patent Application Laid-Open No. 2003-213482    Patent Document 12: Japanese Patent Application Laid-Open No. 2003-213483    Patent Document 13: Japanese Patent Application Laid-Open No. 2004-039315    Non-patent Document 1: T. Narita, M. Shoji, Y. Hisamatsu, D. Yoshida, M. Fukumoto, and S. Hayashi, “Rhenium coating as a diffusion barrier on a nickel-based superalloy in high temperature oxidation”, MATERIALS AT HIGH TEMPERATURES, 18 (S), (2001), 245-251.    Non-patent Document 2: T. Narita, M. Fukumoto, Y. Matsumura, S. Hayashi, A. Kasama, I. Iwanaga, and R. Tanaka, “Development of Re-Based Diffusion Barrier Coatings on Nb-Based Alloys for High Temperature Applications”, NIOBIUM for High Temperature Applications, edited by Y-Won Kim and T. Carneiro, TMS (2004), pp. 99-112.    Non-patent Document 3: Y. Matsumura, M. Fukumoto, S. Hayashi, A. Kasama, I. Iwanaga, R. Tanaka, and T. Narita, “Oxidation Behavior of a Re-Base Diffusion Barrier/ β-NiAl Coating on Nb-5Mo-15W at High Temperatures”, Oxidation of Metals, Vol. 61, Nos. 1/2, (2004), 105-124.